This invention relates to a gas etching device, and more particularly to a gas etching device wherein etching is conducted using an etching gas produced by exiting and dissociating a gas containing therein oxygen atoms and a gas containing therein fluorine atoms.
Conventionally, where, in the process of manufacturing semiconductor such as, for example, IC, a poly-crystalline silicon film, silicon nitride film, silicon dioxide film, molybdenum film, or tungsten film must be finely worked or fabricated, this fine fabrication has been carried out by wet-chemical etching. In recent years, however, an etching technique using the plasma of a gas consisting mainly of, for example, CF.sub.4 has been widely accepted in replacement of the wet-chemical etching.
The apparatus disclosed, for example, in U.S. Pat. No. 3,616,461 is known as an apparatus for conducting such plasma etching. This apparatus comprises a vacuum vessel provided exteriorly with a high frequency coil and a material-placing section provided within said vacuum vessel. In this apparatus, by introducing a freon gas into the vessel and applying a high frequency power having a radio frequency of 13.56 MHz to the high frequency coil, said freon gas is dissociated by discharge to form a plasma of the freon gas, and the material is etched using this plasma. In this apparatus, the condition in which etching proceeds is watched under illumination of a visible light containing therein ultraviolet rays which is emitted from the plasma itself.
Further, a condenser type apparatus is also publicly known wherein the freon gas is dissociated using, instead of the high frequency coil, two electrode plates each having a curved plane.
The etching tecnhique using such apparatus has the following merits as compared with the conventional wet-chemical etching.
(1) Etching of poly-crystalline silicon and silicon nitride can be performed by using a photoresist itself as a mask.
(2) Accordingly, the number of manufacturing process can be decreased.
(3) Harmful effects or nuisances due to chemicals such as, for example, hydrofluoric acid are not produced, which improves the operational environment.
However, what can be said commonly to the above-mentioned known apparatuses is that an etching gas-producing region and a section for placing therein a material to be etched are provided in the same place. For this reason, said known apparatuses pose the following problems.
(1) Due to the radiant heat of the plasma and the actions of exciting light (especially, ultraviolet rays), fluorine ion, etc. a photoresist used as a mask is deteriorated and etched.
(2) Due to oxygen added to a CF.sub.4 gas to an extent of 2 to 4% in order to increase the etching rate, the photoresist ashing proceeds.
(3) Due to the changed particles in the plasma the semiconductor element is damaged.
(4) Due to the actions of electric and magnetic fields positive and negative fluorine ions are ununiformly distributed, which causes the etching material or sample to be ununiformly etched.
(5) During the watching of the etching condition, an undesirable effect of said ultraviolet rays upon the naked eyes is produced.